Short-distance working using a book or a computer are increasing in the 21th century, which is defined as digital and information-orientation after industrialization, thereby threatening the health of eyes. A hydrogel material that is most widely used for a contact lens is a polymer forming a network structure where monomers are bound to each other by a crosslinking agent. A hydrogel used for a contact lens for the first time is poly(2-hydroxyethylmethacrylate (polyHEMA, often referred to as HEMA), developed in 1960's by Wichterle. PolyHEMA is a homopolymer where hydroxyethylmethacrylate monomers are bound to each other in the simplest manner by a crosslinking agent (EGDMA). PolyHEMA is the most widely used for a contact lens for the following reasons: it has a very soft structure and is stable during pH and temperature changes; and a contact lens can be easily prepared by using polyHEMA. However, wearing polyHEMA for a long period of time can cause inconveniences such as corneal edema, congestion and an ache due to a relatively low wettability. Therefore, new products need to be developed to overcome the wettability of polyHEMA. A silicone-rubber-based lens has also been used for the past few years for the therapeutical and pediatric purposes. Despite the superiority in wettability and durability, however, a silicone-rubber lens has various clinical drawbacks. For example, a lens often sticks to an eyeball because tears may not flow through the lens and an extremely high hydrophobicity of a lens frequently induces deposit of lipids on the surface of an eyeball. A silicone hydrogel material is prepared by using a silicone monomer and a hydrogel monomer, and is developed to overcome the drawbacks of a silicone-rubber lens. A silicone ingredient provides a high degree of oxygen permeation, and a hydrogel ingredient increases flexibility, solubility and tear transportation, and therefore promotes the movement of a lens. However, a silicone hydrogel is prepared by using a combination of two different monomers which have heterogeneous properties, i.e., a silicone and a hydrogel monomer, thus requiring a technique for appropriately mixing the two different monomers. Examples of a commercially available silicone-hydrogel lens are Focus Night & Day by CIBA Vision's, PureVision by Bausch & Lomb's and Acuvue Advance by Vistakon's. The Night & Day and the Purevision are approved for an overnight use, and the Acuvue Advance is approved only for a daily use.
It has been reported that the commercially available silicone-hydrogel lens needs to be improved regarding wettability, and there have been attempts made to improve wettability of a lens by modifying the surface of a lens. International patent publication No. WO 06/039466 discloses a process of preparing a silicone hydrogel lens by using various hydrophilic polymers such as polyamide-based, polylactone-based, polyimide-based, or polylactam-based polymers as an internal wetting agent. However, it discloses no wetting effect in a clinic respect, and an internal wetting agent contained in an amount of several percent to several tens of a percent is reported as deteriorating intrinsic properties required in a contact lens.
Further, there have been attempts made to develop a lens care solution for maintaining water content in a silicone hydrogel contact lens. WO 06/009101 discloses a process of preparing a solution comprising polyvinylalcohol (PVA), cellulose and squalene as main ingredients for avoiding the evaporation of moisture. However, it is not effective because the maintenance of moisture varies depending on the hydrophilic functional groups on the surface of a contact lens. Journal of Korean Oph. Opt. Soc. 11, 27 (2006) prepares a lens care solution as a way to maintain wettability of a lens, and compares the resulting contact angles between thus prepared solution and a commercially purchased care solution. Wettability varies depending on the material used for preparing a lens and the type of a care solution. U.S. Pat. No. 4,820,352 discloses a composition comprising a surfactant and sorbic acid as a preserving solution for supplementing wettability of a contact lens. However, it has been reported that this technique can irritate the eyes of a lens wearer and decrease the durability of a lens. Korean patent publication No. 2001-007722 discloses a multi-purpose lens care solution for the purpose of a protein-removing solution, a washing solution and a lens care solution, which comprises a polysaccharide with a molecular weight of 5,000 or higher, non-ionic surfactants and collagen derivatives as main ingredients. The increase in wettability is temporary because it is not the increase achieved by the change in elemental component in a lens.
The present invention has been achieved as a result of attempts made to overcome all the aforementioned problems. That is, wetting properties of a contact lens is increased by the polymerization of an appropriate material in the present invention instead of the surface modification or a lens care solution. The present invention has been completed by finding that a relatively high degree of water content can be maintained for a long period of time by using a contact lens herein.